Well operators around the world are increasingly using wells with multiple tubing strings to improve both injection and production of fluids in a reservoir. Some operators are now using this technology for designing and optimizing thermal, heavy oil recovery. Wells with multiple tubing strings are also being used for isothermal and other operations.
Injection and production control can be based on user-specification of a set of flow rate and pressure constraints at a point in a well where the most constraining limit is determined by a model. Injection and production at a point within the wellbore and not just at the wellhead (the well's output to the surface) is increasingly being employed for (i) recirculation of fluids, for example in steam assisted gravity drainage (SAGD) processes, (ii) for artificial gas lift, (iii) for placement of injection fluids, e.g., steam placement in thermal operations, (iv) for control of production along a wellbore, e.g., in a long horizontal well utilizing sliding tubing strings. Additionally Inflow Control Device (ICD) and Flow Control Valve (FCV) constraint devices are being used to improve production from layers or compartments in a reservoir.
Multiple tubing strings in a well present the dual problem of both design and control. There is need for a rigorous, accurate, and robust method to model these multi-tubing string wells as part of the reservoir simulation stage of “field planning and development” in order to properly design the wells, and in order to improve resource production (i.e., optimal control of the optimal design). In particular, there is a need to control the individual tubing strings with ICD and FCV devices and allow injection and production at various control points along the tubing strings in addition to the single, overall well control.